ER & Golgi Flashcards
what mediates folding of proteins
chaperone proteins
what mediates disulphide bridge formation in proteins
protein disulphide isomerase (PDI)
what is oligomerisation
the assembly of multi-protein complexes
what 3 things are required for ribosome docking
signal peptide/signal sequence (SP), signal recognition particle (SRP), SRP receptor
how do proteins enter the ER lumen
through the translocation channel (translocon)
what occurs during translocation in type 1 proteins
signal sequence is cleaved at the n terminus by signal peptidase
what is the defining property of stop/start transfer sequences
they are hydrophobic so will be found in the ER membrane
how is a hydropathy plot read
the hydrophobic areas represent the hydrophobic domains of signal sequences
what is an internal signal sequence
internal signal sequences exist in the middle of the polypeptide chain rather than the end, so are not cleaved
4 features of a type 1 transmembrane protein
single pass
cleaved signal sequence
stop sequence in the ER membrane
C terminus in cytosol
key difference between type 2 & type 3 TM proteins
orientation, N terminus in cytosol for type 2 protein, C terminus in cytosol for type 3 protein
what determines the orientation of the protein
whether positive amino acid side chains are
in front of or behind the signal sequence. If they are in front of the Signal Sequence then N terminus in cytosol
If behind the signal sequence then C terminus in cytosol
what are type 4 TM proteins
they have 2 or more transmembrane domains (stop/start sequences)
what are the 2 sides of the Golgi and where do they face
cis side faces nucleus
trans side faces nearest plasma membrane
what is the sequence for forward Golgi traffic
er to cis Golgi network to cis cisterna to medial cisterna to trans cisterna to plasma membrane
what is the cisternal progression model
enzymes move sequentially backwards from trans to cis stacks through retrograde vesicle transport, substrates stay in the same compartments
what happens during clatherin mediated endocytosis of LDL
LDL binds to receptor which migrates to clatherin pit
Clathrin coated vesicle is uncoated once inside the cell
`Vesicle binds with endosome of ph5 and receptor releases LDL
Late endosome binds with lysosome and cholesterol, amino acids and small peptides form
Cholesterol is released into cytosol for new membrane formation
how does dynamin work
it polymerises around the vesicle bud neck and hydrolyses GTP to cause a conformational change, this stretches the neck until the bud pinches off
what is the difference between COP1 and COP2
COP1 is the protein coat involved in retrograde enzyme transport, COP2 is the protein coat involved in movement from ER to Golgi. They drive transport in opposite directions
what is the function of SNARES
they are involved in the membrane fusing process, v-snare binds to t-snare to form a tight hydrophobic complex
